Function attributeExists

attributeExists(layerId, attributeName): boolean
JMap.Layer.attributeExists

Returns true if the layer has the given attribute.
Parameters
- layerId: JId
  The JMap layer id
- attributeName: string
  The JMap attribute name
Returns boolean
Throws
Error if layer is not found

Example
```
 // returns true if the attribute named "SPECIES" exist on layer id=4
 JMap.Layer.attributeExists(4, "SPECIES")
```